Configuring EDB Postgres Advanced Server Streaming Replicationinfo.enterprisedb.com/rs/069-ALB-339/images/Tutorial_Configuring... · Configuring EDB Postgres™ Advanced Server

Configuring EDB Postgres™ Advanced Server Streaming Replication

EDB Postgres™ Advanced Server 9.5 formerly Postgres Plus Advanced Server 9.5

March 10, 2016

Copyright © 2016 EnterpriseDB Corporation. All rights reserved.

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Configuring EDB Postgres Advanced Server Streaming Replication

by EnterpriseDB® Corporation


EnterpriseDB Corporation, 34 Crosby Drive, Suite 100, Bedford, MA 01730, USA

T +1 781 357 3390 F +1 978 589 5701 E [email protected] www.enterprisedb.com



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Table of Contents

1 Introduction ................................................................................................................. 4

1.1 Typographical Conventions Used in this Guide ................................................. 5

2 Configuring Streaming Replication ............................................................................ 6

2.1 Configuring the Master Node ............................................................................. 7

2.2 Configuring the Standby Node ......................................................................... 10

2.2.1 Confirming Replication from the Master to Standby ................................... 14

2.3 Manually Invoking Failover ............................................................................. 15



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1 Introduction

Notice: The names for EDB’s products have changed.

The product formerly referred to as Postgres Plus Advanced Server is now referred to as

EDB Postgres Advanced Server (Advanced Server).

The product formerly referred to as Postgres Enterprise Manager (PEM) is now referred

to as EDB Postgres Enterprise Manager (EDB Enterprise Manager).

Until a new version of this documentation is published, wherever you see an earlier

version of a product name, you may substitute it with the current name. Name changes in

software and software outputs will be phased in over time.

EDB Postgres Advanced Server (Advanced Server) includes Streaming Replication

functionality. You can use Streaming Replication to create a high-availability cluster that

enables hot standby. Hot standby allows a standby node to respond to read-only queries

while providing an environment that replicates the data of the master node. The server

streams the change log (WAL records) to ensure that the data on the Standby node is

updated as soon as possible, rather than waiting for a log file to fill before shipping an

update to a standby node.

Streaming Replication does not provide a mechanism to monitor a database for a server

failure or invoke failover. EDB Failover Manager provides the cluster health monitoring,

node/database failure detection, and automatic failover mechanisms needed to create a

high availability solution. For information about EnterpriseDB Failover Manager, please

visit the EnterpriseDB website at:

http://www.enterprisedb.com/products/edb-failover-manager

In the following tutorial, we will walk you through configuring a simple Streaming

Replication scenario with one Master node and one Standby node that enables hot

standby. This tutorial assumes:

You've installed Advanced Server on the Master node of a replication scenario.

You've installed Advanced Server on the Standby node of a replication scenario.

For more information about installing Advanced Server, see the installation guide,

available at:

http://www.enterprisedb.com/products-services-

training/products/documentation/enterpriseedition

http://www.enterprisedb.com/products/edb-failover-manager

http://www.enterprisedb.com/products-services-training/products/documentation/enterpriseedition

http://www.enterprisedb.com/products-services-training/products/documentation/enterpriseedition



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1.1 Typographical Conventions Used in this Guide

Certain typographical conventions are used in this manual to clarify the meaning and

usage of various commands, statements, programs, examples, etc. This section provides a

summary of these conventions.

In the following descriptions a term refers to any word or group of words that are

language keywords, user-supplied values, literals, etc. A term’s exact meaning depends

upon the context in which it is used.

Italic font introduces a new term, typically, in the sentence that defines it for the

first time.

Fixed-width (mono-spaced) font is used for terms that must be given

literally such as SQL commands, specific table and column names used in the

examples, programming language keywords, etc. For example, SELECT * FROM emp;

Italic fixed-width font is used for terms for which the user must

substitute values in actual usage. For example, DELETE FROM table_name;

A vertical pipe | denotes a choice between the terms on either side of the pipe. A

vertical pipe is used to separate two or more alternative terms within square

brackets (optional choices) or braces (one mandatory choice).

Square brackets [ ] denote that one or none of the enclosed terms may be

substituted. For example, [ a | b ] means choose one of “a” or “b” or neither

of the two.

Braces {} denote that exactly one of the enclosed alternatives must be specified.

For example, { a | b } means exactly one of “a” or “b” must be specified.

Ellipses ... denote that the preceding term may be repeated. For example, [ a |

b ] ... means that you may have the sequence, “b a a b a”.



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2 Configuring Streaming Replication

The following section will walk you through the process of configuring a simple two-

node replication scenario that uses streaming replication to replicate data from a Master

node to a Standby node. The replication process for larger scenarios can be complex; for

detailed information about configuration options, please see the PostgreSQL core

documentation, available at:

http://www.postgresql.org/docs/current/static/warm-standby.html#STREAMING-

REPLICATION

In the example that follows, we will use a .pgpass file to enable md5 authentication for

the replication user. For more information about the supported authentication options,

please see the PostgreSQL core documentation at:

http://www.postgresql.org/docs/9.5/static/client-authentication.html

The steps that follow configure a simple streaming replication scenario with one Master

node and one Standby node, each running an installation of Advanced Server. In the

example:

The Master node resides on 192.168.2.206

The Standby node resides on 192.168.2.217

The replication user name is edbrepuser.

The pathnames and commands referenced in the examples are for Advanced Server hosts

that reside on a CentOS 6.5 host – you may have to modify paths and commands for your

configuration.

http://www.postgresql.org/docs/current/static/warm-standby.html%23STREAMING-REPLICATION

http://www.postgresql.org/docs/current/static/warm-standby.html%23STREAMING-REPLICATION

http://www.postgresql.org/docs/9.5/static/client-authentication.html



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2.1 Configuring the Master Node

Connect to the master node of the replication scenario, and modify the pg_hba.conf

file (located in the data directory under your Postgres installation), adding connection

information for the replication user (in our example, edbrepuser):

host replication edbrepuser 192.168.2.217/32 md5

The connection information should specify the address of the Standby node of the

replication scenario, and your preferred authentication method (see Figure 2.1).

Figure 2.1 – Modifying the pg_hba.conf File

Then, modify the postgresql.conf file (located in the data directory, under your

Advanced Server installation), adding the following replication parameter and values to

the end of the file (see Figure 2.2):

wal_level = hot_standby

max_wal_senders = 8

wal_keep_segments = 128

archive_mode = on

archive_command = 'cp %p /tmp/%f'



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Figure 2.2 – Modifying the postgresql.conf File

Save and close the configuration file, and use your platform specific command to restart

the server (see Figure 2.3). For example:

/etc/init.d/ppas-9.5 restart

Figure 2.3 – Restarting the ppas-9.5 Service

Assume the identity of the enterprisedb database superuser:

su – enterprisedb

Then, start a psql session, connecting to the edb database:

psql -d edb



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At the psql command line, create a user with the replication attribute (see Figure

2.4):

CREATE ROLE edbrepuser WITH REPLICATION LOGIN PASSWORD

'password';

Figure 2.4 – Creating the edbrepuser role.

For more information about the options available with the CREATE ROLE command, see

the PostgreSQL core documentation at:

http://www.postgresql.org/docs/9.5/static/sql-createrole.html

http://www.postgresql.org/docs/9.5/static/sql-createrole.html



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2.2 Configuring the Standby Node

Connect to the Standby server, and assume the identity of the database superuser

enterprisedb:

su – enterprisedb

With your choice of editor, create a .pgpass file in the home directory of the

enterprisedb user. The .pgpass file holds the password of the replication user in

plain-text form; if you are using a .pgpass file, you should ensure that only trusted

users have access to the .pgpass file:

Add an entry that specifies connection information for the replication user (see Figure

2.5):

*:5444:*:edbrepuser:password

Figure 2.5 – Modifying the .pgpass File

Save and close the .pgpass file. The server will enforce restrictive permissions on the

.pgpass file; use the following command to change the file permissions:

chmod 600 .pgpass

Relinquish the identity of the database superuser:

exit

Then, assume superuser privileges:

su -

You must stop the database server before replacing the data directory on the Standby

node with the data directory of the Master node (see Figure 2.6). Use the command:

/etc/init.d/ppas-9.5 stop



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Figure 2.6 – Stopping the Database Server

The following command deletes the existing data directory, and any information

currently stored in the data cluster on the Standby node:

rm -rf /opt/PostgresPlus/9.5AS/data

After deleting the data directory on the Standby node, navigate into the bin directory

under your Advanced Server installation:

cd /opt/PostgresPlus/9.5AS/bin

Use the pg_basebackup utility to copy the data directory of the Master node to the

Standby node(see Figure 2.7):

./pg_basebackup –R –D /opt/PostgresPlus/9.5AS/data

--host=192.168.2.206 –-port=5444

--username=edbrepuser --password



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Figure 2.7 – Replacing the data Directory

The call to pg_basebackup specifies the IP address of the Master node and the name of

the replication user created on the Master node. For more information about the options

available with the pg_basebackup utility, see the PostgreSQL core documentation at:

http://www.postgresql.org/docs/9.5/static/app-pgbasebackup.html

When prompted by pg_basebackup, provide the password associated with the

replication user (see Figure 2.8.

Figure 2.8 – Invoking pg_basebackup

After copying the data directory, change ownership of the directory to the database

superuser (enterprisedb):

chown -R enterprisedb /opt/PostgresPlus/9.5AS/data




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Navigate into the data directory:

cd /opt/PostgresPlus/9.5AS /data

With your choice of editor, create a file named recovery.conf( in the

/opt/PostgresPlus/9.xAS/data directory) that includes:

standby_mode = on

primary_conninfo = 'host=192.168.0.5 port=5444

user=edbrepuser password=password'

Please note: the primary_conninfo parameter specifies connection information for the

replication user on the master node of the replication scenario. Save and close the file.

Change ownership of the recovery.conf file to enterprisedb:

chown enterprisedb:enterprisedb recovery.conf

The data file has been copied from the Master node, and will contain the replication

parameters specified on the Master. You must modify the postgresql.conf file on the

Standby node, specifying new values at the end of the file (see Figure 2.9):

wal_level = hot_standby

max_wal_senders = 8

wal_keep_segments = 128

hot_standby = on

Figure 2.9 – Modifying the postgresql.conf File

Save the file and restart the server:

/etc/init.d/ppas-9.5 start



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At this point, the Master node will be replicating data to the Standby node.

For more information about the options available with the pg_basebackup utility, see

the PostgreSQL core documentation at:


2.2.1 Confirming Replication from the Master to Standby

You can confirm that the server is running and replicating by entering the command:

ps -ef | grep postgres

If replication is running, the Standby server will echo:

501 42054 1 0 07:57 pts/1 00:00:00

/opt/PostgresPlus/9.2AS/bin/edb-postgres -D

/opt/PostgresPlus/9.2AS/data

501 42055 42054 0 07:57 ? 00:00:00 postgres: logger process

501 42056 42054 0 07:57 ? 00:00:00 postgres: startup

process recovering 000000010000000000000004

501 42057 42054 0 07:57 ? 00:00:00 postgres: checkpointer

process

501 42058 42054 0 07:57 ? 00:00:00 postgres: writer process

501 42059 42054 0 07:57 ? 00:00:00 postgres: stats

collector process

501 42060 42054 0 07:57 ? 00:00:00 postgres: wal receiver

process streaming 0/4000150

501 42068 42025 0 07:58 pts/1 00:00:00 grep postgres

If you connect to the Standby with the psql client and query the

pg_is_in_recovery() function, the server will reply:

edb=# select pg_is_in_recovery();

pg_is_in_recovery

-------------------

t

(1 row)

Any entries made to the Master node will be replicated to the Standby node. The

Standby node will operate in read-only mode; while you can query the Standby server,

you will not be able to add entries directly to the database that resides on the Standby

node.




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2.3 Manually Invoking Failover

To promote the Standby to become the Master node, assume the identity of the cluster

owner (enterprisedb):

su - enterprisedb

Then, invoke pg_ctl:

/opt/PostgresPlus/9.5AS/bin/pg_ctl promote -D /

opt/PostgresPlus/9.5AS /data/

Then, if you connect to the Standby node with psql, the server will confirm that it is no

longer a standby node:

edb=# select pg_is_in_recovery();

pg_is_in_recovery

-------------------

f

(1 row)

For more information about configuring and using streaming replication, please refer to

Chapter 25 of the PostgreSQL core documentation, available at:

http://www.postgresql.org/docs/current/static/warm-standby.html

http://www.postgresql.org/docs/current/static/warm-standby.html

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Configuring EDB Postgres Advanced Server Streaming Replicationinfo.enterprisedb.com/rs/069-ALB-339/images/Tutorial_Configuring... · Configuring EDB Postgres™ Advanced Server